1. Field of the Invention
Unsaturated polyester resins are widely employed commercially in a variety of reinforced fabrication systems including among others matched metal-die compression, transfer, pultrusion and injection molding. These systems involve curing a formulated compound at high temperatures and pressures in hardened and chrome plated molds. These methods provide the highest volume and highest part uniformity of any thermoset molding technique.
For the purposes of the descriptions dealt with herein, these resins are characterized in terms of systems containing them, and the systems encompass the following types:
1. Resin systems free of reinforcement. This is a resin system utilizes a thermosettable resin that is designed to be used as such or with reinforcement at the high temperatures and pressures utilized in a variety of reinforced fabrication systems including among others matched metal-die compression, transfer, pultrusion and injection molding. When the term "resin system" is used herein, such contemplates a composition using a thermosettable resin that is free of reinforcement, fibrous or non-fibrous, unless it is specifically indicated to contain reinforcement as contemplated in the definitions which follow. PA1 2. "Reinforced resin system" is a resin system in which there is provided a sufficient amount of one or more of fibrous or non-fibrous materials as reinforcing agents that make a positive contribution to the physical properties of the molded product derived from the reinforced resin system. PA1 3. "Non-fiber reinforced resin" system is a resin system in which there is provided a sufficient mount of one or more non-fibrous materials as reinforcing agents that make a positive contribution to the physical properties of the molded product derived from the non-fiber reinforced resin system. A non-fiber reinforced resin system is free of reinforcing mounts of a fiber. PA1 4. "Fiber reinforced resin system" is a resin system in which there is provided a sufficient mount of one or more fibers as reinforcing agents that make a positive contribution to the physical properties of the molded product derived from the fiber reinforced resin system. A fiber reinforced resin system contemplates the optional presence of non-fiber reinforcing agent(s). PA1 The low profile additive is at least partly soluble in the uncured thermosetting resin such as a polyester/styrene solution. As the polyester/styrene mixture crosslinks, the thermoplastic polymer becomes incompatible or less soluble and at least partly comes out of solution. This action causes a volume expansion that compensates for the shrinkage that occurs when the polyester/styrene mixture crosslinks. PA1 1. Reasonable pigment uniformity can be obtained with shrinkage control materials such as polystyrene and polyethylene but only fair shrinkage control can be achieved; e.g., no better than 1.0-1.5 mils/inch shrinkage. PA1 2. Acceptable pigment uniformity cannot be obtained with the very good shrinkage control materials such as the vinyl acetate or acrylate polymers. PA1 3. With a special vinyl acetate--maleic acid copolymer using surface active agents in chemically thickened systems (see U.S. Pat. No. 4,555,534), progress was made towards the goal of very good shrinkage control and uniform pigmentation but in a restricted area. PA1 a. an unsaturated polyester resin, PA1 b. an olefinically unsaturated monomer that is copolymerizable with said unsaturated polyester resin, PA1 c. fiber reinforcement, and PA1 d. a poly(vinyl ether) polymer to control shrinkage. PA1 a. homopolymers or copolymers of conjugated dienes have a weight average molecular weight of 30,000 to 400,000 or higher as described in U.S. Pat. No. 4,020,036. The conjugated dienes contain from 4-12 carbon atoms per molecule such as 1,3-butadiene, isoprene, and the like; PA1 b. epihalohydrin monomer(s), or a copolymer of an epihalohydrin monomer(s) with an oxide monomer(s) having a number average molecular weight (Mn) which varies from about 800 to about 50,000 as described in U.S. Pat. No. 4,101,604; PA1 c. chloroprene polymers including homopolymers of chloroprene and copolymers of chloroprene with sulfur and/or with at least one copolymerizable organic monomer wherein chloroprene constitutes at least 50 weight percent of the organic monomer make-up of the copolymer as described in U.S. Pat. No. 4,161,471; PA1 d. hydrocarbon polymers including ethylene/propylene dipolymers and copolymers of ethylene/propylene and at least one nonconjugated diene, such as ethylene/propylene/hexadiene terpolymers and ethylene/propylene/1,4-hexadiene/norbornadiene, as described in U.S. Pat. No. 4,161,471; PA1 e. conjugated diene butyl elastomers, such as copolymers consisting of from 85 to 99.5% by weight of a C.sub.4 -C.sub.7 is olefin having 4 to 14 carbon atoms, copolymers of isobutylene and isoprene where a major portion of the isoprene units combined therein have conjugated diene unsaturation as described in U.S. Pat. No. 4,160,759.
2. Background to the Field of the Invention
British patent specification 937,703, published Sep. 25, 1963, in characterizing the prior art, describes a casting resin in the following language:
"For the same purpose, it is also known to employ as casting resin a mixture of unsaturated polyesters with a high percentage solution of one or more thermoplastic polymers, such as polystyrene, polyvinyl ether and polyisobutylene in styrene." PA0 "It is also known, for the manufacture of dimensionally accurate moulded elements from unsaturated polyesters and polymerisable compounds, for a portion of the materials first of all to be completely polymerised outside the mould, for the resulting polymers to be comminuted and for the small particles thus obtained to be introduced into the mould. The cavities between the particles are then filled by a liquid mixture of the same components and this mixture is thereafter polymerised." PA0 1. Polymerization initiators such as t-butyl hydroperoxide, t-butyl perbenzoate, benzoyl peroxide, t-butyl peroctoate, methyl ethyl ketone peroxide, and others know to the art. The polymerization initiator is employed in a catalytically effective amount, such as from about 0.3 to about 2 to 3 weight percent, based on the weight of the polyester plus monomer plus low profile additive; PA0 2. Fillers such as clay, hydrate alumina silica, calcium carbonate and others known to the art; PA0 3. Reinforcing fillers such as glass fibers or fabrics, carbon fibers and fabrics, aramide fibers and fabrics, asbestos fibers or fabrics, polypropylene, acrylonitrile/vinyl chloride copolymers, PAN fibers and fabrics; PA0 4. Mold release agents or lubricants, such as zinc stearate, calcium stearate, calcium stearate, and others known to the art; and PA0 5. Rubbers or elastomers such as: PA0 1. Unsaturated Polyester Resin-1 is a polyester resin that is manufactured by North American Rockwell and sold under the trade designation of NR-3529. It is the condensation product of maleic anhydride and propylene glycol and contains approximately 35 weight percent of styrene. PA0 2. Unsaturated Polyester Resin-2 (alkyd) is a polyester resin in which the the alkyd portion of an unsaturated polyester resin/styrene solution is a resin produced by Freeman Chemical as Stypol 40-2955. This alkyd is based on 0.25 moles of isophthalic acid, 0.75 mole of maleic anhydride and 1.10 moles of propylene glycol. PA0 3. Unsaturated Polyester Resin-3 is the resin of unsaturated polyester resin-2 in its commercial form containing approximately 35 weight percent of styrene. PA0 4. Unsaturated Polyester Resin-4 is a polyester resin based on the condensation product of maleic anhydride and propylene glycol and containing approximately 37 weight percent of styrene monomer which is sold by Owens Corning Fiberglass as CX-1652. PA0 5. Poly(vinyl ethyl ether)-1 is a poly(vinyl ethyl ether) having a molecular weight of about 2,000,000. PA0 6. Poly(vinyl ether)-2 is a poly (vinyl ethyl ether) polymer of approximate molecular weight of M.sub.n --40,000, M.sub.w --150,000. It is sold by BASF as Lutanol.TM. A-50. PA0 7. Poly(vinyl ether)-3 is a poly (vinyl isobutyl ether) polymer of approximate molecular weight of M.sub.n --10,000, M.sub.w --23,000. It is sold by BASF as Lutanol.TM. I-30. PA0 8. Poly(vinyl ether) Polymer-4--a poly (vinyl isobutyl ether) polymer of approximate molecular weight of M.sub.n --22,000, M.sub.w --300,000. It is sold by BASF as Lutanol.TM. I-60. PA0 9. "Polystyrene" is a rubber modified material manufactured by Union Carbide as LPS-80 for use as a shrink control additive. PA0 10. Poly (methyl methacrylate) is a carboxyl containing polymer manufactured by Rohm and Haas as P-701 for use as a shrink control additive. PA0 11. Poly (vinyl acetate)-1 is a carboxyl containing vinyl acetate polymer manufactured by Union Carbide as LP-40A for use as a shrink control additive. PA0 12. Ethylene-Vinyl Acetate Copolymer-1 is a 40 weight percent ethylene--60 weight percent vinyl acetate copolymer manufactured by IGF Bayer AG as Levapren.TM. 450. PA0 13. Al-Sil-Ate LO is a clay filler from Freeport-Kaolin. PA0 14. ASP-400 is a clay filler from Engelhard. PA0 15. L-256 is a peroxide catalyst from Lucidol. PA0 16. Zelec UN is a mold release agent from DuPont. PA0 17. OCF 498AA is a chopped fiberglass manufactured by Owens Corning Fiberglass. PA0 18. PPG 303 is a chopped fiberglass manufactured by PPG Industries. PA0 19. PPG 3075 is a chopped fiberglass manufactured by PPG Industries. PA0 20. Black pigment dispersion-1 is a carbon black dispersion at about 30 weight percent sold by Plasticolors, Inc. as CM-2015. PA0 21. MgO Dispersion-1 is a magnesium oxide dispersion at about 33 weight percent is an unsaturated polyester carrier resin sold by USS Chemicals as Modifier M. PA0 22. Hydrated alumina is Alcoa C-331 grade.
The British specification is not dear as to the relationship of this casting resin to the molding procedure recited in the preceding paragraph, which reads as follows:
This British patent specification fails to depict reinforced resin systems, especially fiber reinforced resin systems, the predominant direction of the unsaturated polyester molding resin art. Since the date of this specification, a complex art relating to the molding of unsaturated polyester resins with reinforcing fibers has developed. This art has emerged to a level of significant commercial proportions with many commercial items being made by molding, as contrasted to casting, of unsaturated polyester resins in combination with reinforcing fibers which are part of complex systems. The specifications that have emerged for such unsaturated polyester resin systems so significantly transcend the early developments in the art of molding, as reflected by the British specification, that little relationship between that work and today's technical demands exists.
One technical improvement that has made a significant contribution to commercial unsaturated polyester fiber reinforced molding technology is the use of low profile additives to reduce shrinkage during the curing reaction and to thereby improve dimensional stability and surface smoothness (through good mold reproduction). Low profile additives are typically described as thermoplastic polymers such as vinyl acetate polymers, acrylic polymers, polystyrene, saturated polyesters, polycaprolactones, polyurethanes, cellulose acetate butyrate, polyalkylene oxides, and others. However, the most significant of them are the vinyl acetate polymers and the acrylic polymers.
References are made to the following United States Patents as examples of this technology: U.S. Pat. Nos. 3,718,714; 3,549,586; 3,668,178; 4,284,736; 3,701,748; 3,772,241; 3,503,921; 3,736,728; 3,489,707; 3,988,388; 3,665,055; 4,491,642; 4,374,215; 4,525,498; and 4,555,534.
There are a number of theories that seek to explain the low profile or anti-shrinkage action of these polymers, but the one that seems to best explain the phenomenon is the following:.
A major advance in commercial thermosetting molding technology was the introduction a number of years ago of chemically thickened systems. Chemical thickening is always employed in sheet molding compounds ("SMC"), and is increasingly being used in bulk molding compounds ("BMC"). In such systems, an alkaline material such as magnesium oxide or magnesium hydroxide is added to, for example, an uncured polyester along with fillers, glass fiber, and other standard materials. The alkaline material interacts with residual acidity in the polyester to build viscosity. The thickened system is relatively tack free and easy to handle, and the high viscosity carries the glass fiber reinforcement to the extremities of the mold during crosslinking of the system. Thus, the use of thickened systems has made a major contribution to the commercial expansion of polyester molding.
However, there are cases where chemical thickening is undesirable because it reduces the shelf life of the molding compound or because various molding techniques such as injection molding can be sensitive to viscosity changes in the molding material.
For all of the advancements in low shrink or low profile molding technology one problem has defied an optimum solution. That is the uneven distribution of pigment when the molding compound is cured resulting in a non-uniform, lightened and "marbled" appearance which is unacceptable for many applications. To be able to achieve this color uniformity could preclude having to paint some parts molded from these materials and would also make the utility of these molding materials possible in other applications.
The history of the study of this problem has shown:
No general polymer type has been identified that can combine the excellent shrinkage control properties and uniform pigmentation, particularly across chemically thickened and unthickened formulations.